Barrier/liner films are critical components in multilevel interconnect technology, particularly important for Cu and Al metalization. Cu is known to be able to diffuse into Si, SiO.sub.2 and other dielectric films. Al in contact with Si or suicides have problems associated with "junction-spiking". Good gap-fill of Cu/Al also requires a proper liner to help reflow. High quality barrier/liner films are therefore essential for the success of both Cu and Al metalization.
The most common barrier films used in microelectronics industry today are TiN-based thin films. At present, TiN-based barrier films are mainly prepared by physical vapor deposition (PVD) using reactive sputtering, with or without collimation. However, sputtering is a line-of-sight technique and produces films with poor step coverage. As the minimum feature size shrinks and the aspect ratio of contact/via/trench increases, processes that produce conformal films are required. Another problem associated with PVD films is that the films have columnar structures and provide easy diffusion paths. This is particularly severe when device minimum feature continues to shrink and thickness of barrier/liners continues to decrease.
Chemical-vapor-deposition (CVD) processes deposit films with improved step coverage. Although much work has been reported on CVD barrier films, many of the reported processes cannot satisfy the strict requirements needed for semiconductor device fabrication. To be production-worthy, a process should produce high quality films with low defect density (low particle counts), have adequate throughput, and use highly reliable equipment.
Two types of CVD processes are used currently: one based on inorganic precursors, such as TiCl.sub.4 /NH.sub.3, and the other based on metal-organic precursors, such as tetrakis(dimethylamino)-titanium (TDMAT) and tetrakis(diethylamino)-titanium (TDEAT). The inorganic based processes require high deposition temperatures (&gt;550.degree. C.), leave corrosive impurities (e.g. Cl) in the films and have problems associated with particulate formation (e.g. NH.sub.4 Cl). CVD processes using metal-organic precursors (MOCVD) still are not well-established. Thermal decomposition of TDMAT or TDEAT produces films with high resistivity, which increases upon exposure to air. Adding NH.sub.3 into the reactant mixture improves the resistivity; however, the step coverage is adversely affected and NH.sub.3 addition introduces gas phase reactions, a potential source for particle generation. An in-situ plasma treatment of TDMAT thermal decomposed films was also reported. However, this process has very low throughput due to limited penetration depth of plasma and requires special hardware.